a Phosphorylating respiration of liver and kidney mitochondria upon convergent electron flow to coenzyme Q pool via CI and CII in presence of ADP (CI&CII-linked OXPHOS). Mitochondrial NADH was generated with a substrate cocktail comprising malate, pyruvate, and glutamate. Succinate served as direct substrate for CII. b Proton leak upon high membrane potential state was assessed after inhibition of ATP synthase by oligomycin. c Subsequently, a protonophore, FCCP, was titrated to assess the maximal uncoupled electron transfer (ET) capacity. Maximal oxygen consumption capacity, as measured using ascorbate and TMPD as substrates for the terminal oxidase (CIV), was set as the reference state for the oxygen fluxes (a–c). Supplementary Fig. 9 shows the same data relative to mitochondrial protein. d, e ET coupling efficiency (1−L/E) as calculated from oligomycin-induced leak respiration (L) and uncoupler-induced maximal CI&CII-linked electron transfer capacity (E). Samples collected at P30 from backcrossed mice were used for the analyses. Supplementary Fig. 7 shows similar analysis from F1 hybrid mice. Statistics: One-way ANOVA followed by planned comparisons. Error bars represent 95% CI of the mean.